Paving mixture and process of preparing same



Patented June 10, 1930 UNITED STATES PATENT" OFFICE EDWIN O. WALLACE, OF NEWTON, MASSACHUSETTS PAVING MIXTURE AND PROCESS OF PREPARING SAME 1T0 Drawing.

In addition to the'so-calleil rock asphalt which consists of' rocks more or less thoroughly impregnated with bitumemthere are many deposits of bitumen coated sand'sometimes 5 referred to as tar sands which although the particles are not minerally bound are frequently classed under the broad term asphalt rock. In such sands there is more or less agglutination due to the cementing qualities of the bitumen with which the sand particles are coated, but when warmed, separation into substantially individual sand particlesreadily occurs.

Whether or not the sand particles are minerally bound (to form a rock) or merely agglutinated by the bitumen with which they are coated, there is a vast difference in both the quality and quantity of the bitumen found in such deposits. When free from the mineral matter, the bitumen may range from very hard, brittle material to that of a soft, buttery consistency, lWhlGh is little more than an oil.

Great variation both in the percentage of izing asphalt rock impregnated with bitumen 4 results. The presentapplication applies to a method of using bituminous sands and arenaceous rocks, generally impregnated with soft bitumen, which material requires strengthening or stiffening to render it satisfactory for paving work. It'also serves to correct grading of the sand particles so as to produce better graded mixtures.

In native bituminous sands it is in most cases found after the extraction of the bituwith limestone of certain grade, thoroughly which requires softening to give satisfactory Application filed November 5, 1928. Serial No. 317,496.

men, that the residue is very largely composed of substantially uniform sized particles which may be coarse, medium or fine, but seldom consists of a well graded mixture of coarse, medium and fine particles.

Attempts have been made to select materials from different deposits or various sections of the same deposit and to combine them in certain proportions to produce a mixture having the desired grading of coarse to fine particles.

From the commercial standpoint such methods are prohibitive as the cost of selecting and combining the various grades of material required is too great for successful op;

eration on a commercial scale; furthermore in order to produce satisfactory paving mixture, it is necessary to control within reasonable, limits the consistencv as well as the amo nt of bitumen in the mixture. All these 7 desirable results may be obtained in a practical way by the method herein described. The process consists in thoroughly distributing certain proportions of heated sand particles which have been coated with bitumen of hard consistency, throughout a quan tity of native bituminous sand or comminuted asphalt rock containing bitumen of softer consistency.

I The proportions in which the native material and the heated bituminous coated sand particles are combined will vary widely according to the conditions. In some instances the native material may not constitute more than 25% of the finished product, in others it may constitute or more, but as a general rule it will fall within the limits of The correction of the grading of the mineral particles of the native material is of great importance and easily accomplished by my method.

When the mineral particles of the native material consist largely of fine material, the sand mixture added thereto should be relatively coarse and conversely, when the mineral particles of native material are relatively coarse, the sand mixture added thereto should be finer. On the other hand when, as is frequently the case, the native material consists oi. substantially uniform medium sized particles the mixture added thereto should consist of coarse and fine mineral particles substantially free from medium sized particles of which the native material contains an excess. The following examples may be given to show the change wrought in native material by this method of procedure.

A representative sample of a supply of bituminous sand was found to consist of very fine sand carrying 12% bitumen which penetrated 120 at 77 F. Sixty parts by weight of this native material was combined with forty parts of a prepared mixture carrying 8% of bitumen penetrating 30. at 77 F. the mineral portion of which consisted of coarse sand and a small proportion of dust.

Analyses of the native sand and the prepared mixture and the combination of the two are given below Product Native Prepared QQ gSJ material mixture pared mix ture Bitumen 12% 8% 10% 2X) mesh dust... 22. 5 8 17 100 mesh fine sand 48 4 31 80 mesh sand- 5 12 8 50 mesh sand- 5. 3 20 11 40 mesh sand. 1. 8 16 8 30 mesh sand 1. 8 12 6 20 mesh sand 0. 6 12 5 10 mesh sand.-. 1. 8 8 4 On 1 0 1. 0 Pen. ol bitumen 120 30 54 Native Prepared ggi g material mixture parts Bitumen Dust (200 mesh) Finesand (80-100) Coarse sand 00-20-30)" Pen. of bitumen In both the above cited cases the physical properties ot the product were qu te difierent from that of the native material or the mixture prepared to mix with it.

I am fully aware that attempts have been made to harden bituminous sands by adding thereto a small proportion of very hardasphalt in a powdered or melted condition.

The very small proportion of hard asphalt required under such conditions precludes the possibility of its thorough distribution throughout the mass of native material and without thorough distribution the very purpose for which it is added is defeated.

On the other hand by the rocess herein described the intimate commmgling of the mineral particles coated with hard bitumen with the particles of native material coated with softer bitumen serves to distribute the hard bitumen throughout the native material and yields a product the physical characteristics of which are quite different from either of the component compositions, native or artificial.

By this method of procedure, bychanging the composition of the prepared mixture and the proportion in which it is mixed with native material, it is possible to produce suitable paving mixtures from an infinite variety of native bituminous sands and rock asphalts which have heretofore been unavailable for use in paving work.

By the term sand-like material, I mean either sand or comminuted rock, gravel, slag, etc., of a size of particles similar to the size of particles of sand.

I claim z 1. The method of producing improved pavmg mixtures from native bituminous sands and asphalt rock which comprises controlling the quantity of and the consistency of the bitumen and correcting the grading of the mineral element by preparing a suitable mixture of heated sand or fine stone particles so graded as to supply the deficiency of certain sizes of the, native material and combining it with heated bituminous cement the proportion of which is less and the consistency of which is harder than the proportion and consistency of the bitumen in the native material, then thoroughly commingling the prepared mixture and the native bituminous sand or asphalt rock to produce a composition suitable for paving purposes having a well graded aggregate and a bituminous cementing medium of harder consistency than the bitumen contained in the native mate-- rial.

2. The method of producing a bituminous mixture suitable for paving purposes with a cementing medium harder than the bitumen contained in native bituminous sand or asphalt rock which comprises correction of the grading of the mineral elements of the na tive material by adding thereto and commingling therewith an artificially prepared heated mixture of sand or fine stone particles of difi'erent size than those of the native material and asphalt cement of harder consistency than the bituminous cement of the native material, the proportions in which the native material and the prepared mixture are combined being controlled by the amount and consistency of the bitumen and the mesh composition of the mineral element of the native material and of the prepared mixture.

3. A bituminous mixture suitable for paving purposes having .compositlon substantially within the following limits:

Soluble in CS (i-12% 200 mesh material (filler) 520 Pass 80 on 200 9-40 Pass 40 on so 4018 Pass 10 on 40 ..i 3010 Pass on 10 10 0 and which comprises native bituminous sand 15 or comminuted asphalt rock, and an artificially prepared mixture th roughly commingled therewith, the artificially prepared mixture being of different mesh composition than the native material and containing 20 bitumen of harder consistency than the bitumen contained in the native material.

In testimony whereof I aflix my signature.

EDWIN C. WALLACE. 

